The basic structure of advanced video compression standards may divide the video frames into two main types of frames: independent frames, also known as INTRA frames (or I-frames) and dependent frames, also known as INTER frames (or predicted (P) and/or bidirectionally predicted (B) frames).
INTER frames may be smaller than INTRA frames because they are compressed with respect to other frames. INTER frames may be expressed in terms of or in relation to one or more neighboring frames, and may contain only the difference between the current motion compensated frame and a reference frame.
Each INTER frame may be divided in to smaller segments, which are called macro blocks (MB). In the encoding process, the encoder may search for similar MBs in the reference frame. The spatial displacement between the location of the MB in the current frame and the location of the most similar segment in the reference frame is called a motion vector (MV). Each encoded MB may be built out of two main parts: the MV, and the difference from the reference segment.
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